The present invention relates to a new and improved grinding machine and method of operating the machine to grind a workpiece.
Grinding machines having wheels which are movable along a path extending at an acute angle to the axis of rotation of a workpiece are well known. Some of these known grinding machines are disclosed in U.S. Pat. Nos. 2,813,379; 2,955,391; 3,145,507; and 3,762,102. During operation of at least some of these known grinding machines, shoulder and side surfaces of the workpiece have been plunge ground by moving the grinding wheel toward the axis of rotation of the workpiece. As the grinding wheel moves inwardly toward the workpiece, an annular face surface of the grinding wheel is effective to grind a cylindrical side surface of a workpiece to a desired diameter. Simultaneously therewith, an annular edge surface on the grinding wheel is effective to grind a radially extending shoulder surface.
During this plunge grind stroke of a known grinding machine, only a relatively short axially extending portion of the workpiece is ground by the face surface of the grinding wheel. If it is desired to grind an axially extending side portion having a length which is greater than the size of the face surface of the grinding wheel, the grinding wheel is moved away from the workpiece shoulder after completing the plunge grind stroke. The workpiece is then moved along its axis of rotation through a series of traverse grind strokes. During these traverse grind strokes, the edge surface of the grinding wheel is spaced apart from the shoulder surface of the workpiece since the shoulder surface has already been ground to the desired depth. Thus during the traverse grind strokes, only the face surface of the grinding wheel is effective to grind the side surface of a workpiece.
Various control systems have been utilized in association with grinding machines. In addition to the controls disclosed in the forementioned U.S. patents, other grinding control systems are disclosed in the U.S. Pat. Nos. 2,701,494; 3,634,978; 3,818,642; 3,820,287; and 3,919,614. Although various control systems have been utilized in association with grinding machines having wheels which move along a path extending at an acute angle to the axis of rotation of the workpiece, it is believed that these controls have included a register which stores data corresponding to the position of the grinding wheel along its path of movement. However, the positions of both the edge and face surfaces of a grinding wheel vary relative to the workpiece as the grinding wheel moves along a path which extends at an acute angle to the axis of rotation of the workpiece. Therefore, data indicating the position of the grinding wheel along its path of movement does not itself indicate the positions of the edge and face surfaces of the grinding wheel relative to a radially extending shoulder surface and an axially extending side surface of the workpiece.
Dressing of the face and edge surfaces of a grinding wheel which moves along a path extending at an acute angle to the axis of rotation of a workpiece, varies the position of the face surface of the grinding wheel relative to the axially extending side surface of the workpiece and the position of the edge surface of the grinding wheel relative to a radially extending shoulder surface of the workpiece. Therefore, after a wheel dressing operation, the controls for such a grinding wheel must be adjusted to compensate for the amount of material removed from the grinding wheel. This has previously been done by adjusting the data stored in a register indicating the position of the grinding wheel along its angled path of movement relative to the workpiece. It is believed that prior control systems have not provided for the storing and changing of data corresponding to the distance between the edge and face surfaces of the grinding wheel and a radially extending shoulder surface of the workpiece to thereby compensate for the dressing of the grinding wheel. An apparatus for dressing the face and edge surfaces of a grinding wheel which moves along a path extending at an acute angle to the axis of rotation of a workpiece is disclosed in U.S. Pat. No. 3,916,581. Various other devices for dressing grinding wheels are disclosed in U.S. Pat. Nos. 2,894,360; 2,895,265; 2,900,974 and 2,907,315.
The surfaces on a workpiece have previously been accurately located relative to a grinding wheel by the use of a probe which engages a reference surface in a manner similar to that disclosed in U.S. Pat. No. 3,885,734. With these known locator assemblies, the workpiece must be moved to accurately position the reference surface in a predetermined location. Any error in locating the reference surface relative to the predetermined location can result in an error in the grinding of the workpiece. Of course, locating a reference surface exactly in a predetermined reference plane can be a time consuming process.
In addition to encountering difficulty in accurately locating a reference surface on a workpiece relative to the axis of rotation of the workpiece, difficulty has been encountered in moving a grinding wheel through relatively small increments of distance relative to a workpiece. With certain known grinding machines, the grinding wheel may not move through a relatively small distance toward a workpiece when an operator initially actuates the controls. Upon noting the lack of movement of the grinding wheel toward the workpiece, the operator may again actuate the controls. After repeated actuation of the controls, the grinding wheel may move through a relatively large distance toward the axis of rotation of the workpiece. Of course, the resulting movement of the grinding wheel through a relatively large distance could result in a misshaping of the workpiece.
Difficulty has been encountered in removing the same incremental depth of material upon each revolution of the workpiece at locations having different diameters. Thus, the feed rate of a grinding wheel may be such as to remove a small increment of metal during each revolution of a portion of a workpiece having a small diameter. Although it may be desired to remove the same depth of metal during each revolution of a relatively large diameter portion of the workpiece, the feed rates of certain known grinding machines have been such as to effect the removal of a different incremental depth of material on each revolution of a relatively large diameter portion of the workpiece. This is because when the rate of workpiece rotation is adjusted for different diameter portions of a workpiece, the feed rates of the grinding wheel have been manually set to provide a number of inches per minute of wheel feed rate. In setting the wheel feed rate, different incremental depths of material have been removed from the workpiece upon each revolution of the different size portions of the workpiece.
Since the grinding wheel rotates at a relatively high speed and can break when subjected to excessive forces, caution must be exercised in operating a grinding machine. Thus, during rapid movement of a grinding wheel relative to the workpiece and during rapid movement of the workpiece relative to the grinding wheel, care must be exercised to prevent engagement of the grinding wheel with the workpiece and the resulting application of excessive forces to the grinding wheel. In addition, during a grinding operation excessive feed rates of a grinding wheel can result in breaking of the grinding wheel.
It is contemplated that problems could be encountered during operation of a grinding machine if for some unforeseen reason, such as maltreatment of the grinding machine, a malfunction should occur in the wheel or workpiece positioning drive train or controls during operation of the grinding machine. Breakage of a wheel positioning drive shaft would render the machine controls ineffective to move the grinding wheel away from the workpiece. Similarly, breakage of a workpiece positioning drive shaft would render the machine controls ineffective to move a shoulder on the workpiece away from the grinding wheel.